Matrix Stimulation

The evolution of horizontal drilling and multistage completions has changed matrix stimulation from the “more acid, better result” belief to effective lateral distribution and deeper penetration with less acid.

Large-gallon-per-foot-based ­treatment became impractical and unnecessary. The constant remains that drilling is blamed for causing formation damage; therefore, matrix stimulation is needed. Underbalanced coiled-tubing drilling aimed at changing this constant, however, has its own drawbacks.

For certain lithologies, acid tunneling can be an attractive alternative to rotary-bit drilling. Though the technology was proposed many years ago, its use has been limited. Hardware to control the drilling direction, fluids to dissolve the formation rock efficiently, and jetting dynamics to optimize the rate of penetration have been pushed forward progressively. The goal of stimulation while drilling finally may be achievable.

Of course, not all reservoir rock types are readily soluble in chemicals. Cracking the reservoir rock will continue to be the preferred process for sandstone. The first mechanism we think of for rock cracking is hydraulics. Unless full-fledged hydraulic fracturing is required, using high-energy pulses induced by propellant or other chemical reactions can produce sufficient pressure to break the rock past the near-wellbore formation damage. Perfecting the control and job design can lead to efficiency and broader implementation.

One question we often ask in the matrix-stimulation domain is “what’s new?” It almost seems that the products and technologies of yesterday have been brought out again and again with minor twists. Indeed, it is amazing how many “new technologies” actually have been around for decades.

While most of the industry is busy handling daily operations and logistics, it is encouraging to see universities, government-­supported research and development institutes, and even some large service and operating companies studying the science behind the products and technologies. Advanced multiscale, multiphysics mathematical models are used to optimize particle bridging for diverting efficiency; large-scale experimental setups are used to gain insights into differential etching patterns during acid fracturing caused by viscous fingering and heterogeneous reactions, perforation penetration in realistic geometry and stresses, and other phenomena that could not be observed by small-scale laboratory testing. These studies help us appreciate the ingenuity of our predecessors and help us fit the technologies to the right applications better.

Frank Chang, SPE, is a petroleum engineering consultant in production technology with Saudi Aramco, which he joined in 2012. He manages a portfolio of projects focused on developing new technologies in hydraulic fracturing, carbonate stimulation, formation-damage removal, corrosion and scale mitigation, and sand control. Chang started his career with Stimlab in 1992 after earning a PhD degree in petroleum engineering from the University of Oklahoma. He joined Schlumberger in 1996. Chang progressed from development engineer to engineering adviser during his 16-year tenure at Schlumberger, where he was involved in development of several new products and technologies in sand control, fracturing, acidizing, and perforating. He is an author of the SPE acidizing monograph published in 2016. Chang holds 28 patents, is an author of more than 50 technical papers, and was named an SPE “A Peer Apart” honoree in 2015. He serves as Executive Editor of the SPE Production & Operations journal and is a member of the JPT Editorial Committee. Chang can be reached at fakuen.chang@aramco.com.

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